JP2002210349A - Supercritical wet oxidation method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for the supercritical wet oxidation of a residue mixture containing particles comprising organic and inorganic components by suspending the organic and inorganic components in water, bringing the water into a near-critical or supercritical state, and passing the water in this state through a tubular reactor and to provide an apparatus therefore. SOLUTION: A tubular reactor (6) is constructed so that an organic component may not be substantially oxidized therein and may be substantially dissolved in water. The starting material of the tubular reactor in a near- or super-critical state is passed through a second reactor (8) constructed so that it may have a ratio of its inside surface area to its volume markedly lower than that of the reactor (6), and the organic component may be substantially completely oxidized in its inside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for suspending organic and inorganic components in water, bringing the water into a near-critical or supercritical state,
Further, the present invention relates to a method and an apparatus for supercritical wet oxidation of a residual substance mixture containing particles composed of the organic and inorganic components by passing through a tubular reactor in this state.

[0002]

2. Description of the Related Art Supercritical water has very good properties as a solvent for organic materials and also as a reaction medium. This property can be exploited for the hydrothermal treatment of residue mixtures, for example crushed lightweight fractions of the automotive industry or electronics scrap.

[0003] The first known reactor concept is a fixed bed reactor in which the residue mixture is present as a solid in the sediment. In this case, however, only relatively small quantities can be charged so that the reaction temperature does not rise significantly in this unsteady operation. Fixed bed reactors often must be opened and exposed to kinetic loads. The temperature and the concentration are unevenly distributed and the material transport is hampered by solid packing.

The second reactor concept is a suspension tube reactor. Within the scope of the BMBF transfer plan for the preparation and use of electronic component scraps by supercritical wet oxidation (transport standards 01RK9632 / 8 and 01RK9633 /
At 0), an experimental apparatus is constructed in which near-critical or supercritical water flows through a reactor in the form of a horizontal, elongated tube, in which residual substance particles are suspended. And it is kept floating by the high flow velocity and thus the turbulence associated therewith. In a tubular reactor, the organic components are dissolved in water, decomposed and oxidized.

[0005] Tubular reactors can indeed operate continuously, but not only do the reactor walls suffer from attrition due to rapidly moving residual material particles, but also at the same time near-critical or supercritical water. And components contained therein,
In particular, they suffer from corrosion due to already decomposed organic components. Another problem is the unfavorable space-time yield:
Tubular reactors need to be constructed relatively long so that the residual material mixture stays inside for a sufficient length and complete decomposition takes place.

[0006]

This problem is solved by a method and a device according to the independent claims.

In accordance with the present invention, a tubular reactor is used to separate and treat a complex mixture of residual materials utilizing the properties of supercritical water, wherein the organic material-containing components are chemically decomposed. , A second, rather swollen reactor connected back and forth and running continuously.

[0008] Splitting into two reactors involves two steps along the process chain: heat input and output, attrition and corrosion, space and energy demand, legal concept and safety.
Combines two individual benefits.

The dissolution of the organic components takes place substantially in the fluidized bed, and the oxidation of the organic components takes place substantially in the second reactor. Hydrolysis or decomposition of the organic component,
It can already be carried out in a tubular reactor. However, this is not important if the hydrolysis is carried out for the first time, partially or mainly in the second reactor. The various processes during the decomposition of the organic components, namely the dissolution, hydrolysis or oxidation, cannot indeed be separated from one another in practice.
For they run partly in parallel with each other. However, by a suitable design of both reactors, it is possible to ensure that the dissolution takes place entirely predominantly in the fluidized bed and that the oxidation takes place almost completely in the second reactor.

[0010] Since dissolution generally takes place faster than hydrolysis and much more rapidly than oxidation, tubular reactors are more efficient than prior art tubular reactors in which all three of the above reactions take place. It can be very short. The second reactor is in any case relatively compact. Thus, the invention as a whole makes possible a significantly more compact design than tubular reactors based on the prior art.

[0011] The tube reactor is significantly shorter than the tube reactor according to the prior art, in which all three of the abovementioned reactions proceed, so that the problem of plugging is avoided.

[0012] In conventional tubular reactors, the energy demand is significant because water is conveyed at high speed through long, narrow tubes with the particles suspended therein. In the significantly shorter tube reactors of the present invention, the energy demand for transport is significant. The energy savings make the excess cost of transporting the second reactor rather rather unnecessary. This is because transporting through an inflated tank requires relatively little energy in any case.

Since only a small amount of hydrolysis and oxidation takes place in the tubular reactor, the material of the tubular reactor is subject to attrition, but only slightly corrosive. In the second reactor, the flow rates are considerably lower than in the tubular reactor, due to the rather expanded construction, so that the material of the second reactor is certainly corrosive, but is subject to a slight attrition load. It's just Near the critical state of water, it is significantly easier to find materials that are either corrosion resistant or abrasion resistant than those that are corrosion resistant and also abrasion resistant under the governing conditions. This greatly simplifies the choice of reactor materials and can significantly extend the useful life of both reactors.

In order to ensure complete oxidation of all organic components, an oxidizing agent such as, for example, oxygen can be added to the process water from somewhere in front of the second reactor. If the oxidant is first fed before the second reactor or directly to the second reactor, it also reduces the corrosion in the first reactor.

The device according to the invention is particularly suitable for treating residual substances having a high halogen content. The presence of halogen generally results in particularly severe corrosion. However, in the present invention, in the tubular reactor, the halogen is still well bound to the polymer chain,
In addition, the salt generated from the halogen precipitates rapidly. This is because the inert substances present in the residue mixture act as germs.

The tubular reactor is preferably a PFR (Plug F
low Reactor, a long, narrow tube reactor characterized by a high flow rate. Due to the turbulence associated therewith, good radial mixing generally takes place, which mixing prevents sedimentation of the particles. In contrast, the ideal PFR is reverse mixing,
Therefore, no axial mixing is performed. Due to its large ratio of internal surface area to volume, heat can be supplied and extracted very well. Accordingly, locally continuous reactions are avoided and a uniform temperature and concentration profile is formed over the entire length of the PFR.

The second reactor is preferably a CSTR (Cont
Infrequently Stirred Tank Reactor, ie, an inflated tank with a stirring device. The stirrer causes thorough mixing of the liquid components in the entire reaction chamber. Therefore, the concentration and temperature inside the reactor are positionally constant. For small ratios of internal surface area to volume, heat can certainly only be introduced or removed relatively slowly, but most of the heat of reaction can already be withdrawn in the tubular reactor .
If necessary, cold water can be supplied to the second reactor to reduce the exotherm for further reactions.

In the second reactor, a relatively long residence time which allows complete decomposition of the organic components can be realized with a small structural volume. However, based on thorough mixing during agitation, the dwell time should not be too long.

Based on the expanded shape of the second reactor, special measures can be taken to reduce the corrosive load of the reactor material. For example, the reactor walls can be cooled while the reaction is performed primarily in the hot core zone.

In the second reactor, it is not necessary to consider settling. This is because the inorganic substances still present, ie, inert substances, precipitated salts and other solids, are not important for hydrolysis and oxidation. Despite agitation in the second reactor, some demixing of the particles does take place, but this is likewise not critical. The particles can easily and more rapidly settle out of the reactor and be separated off later. Alternatively, the particles may be separated by a separator before they enter the second reactor. However, in this case, the separator is also
It must be able to withstand conditions that are dominated near the critical point of water.

The process according to the invention of supercritical wet oxidation to chemically decompose residual substances is advantageously used not only for the treatment of electronics scrap and wastewater and sludge, but also for crushed lightweight from automobile recycling. It is also characterized by being suitable for the treatment of fractions. The last residual substance mixture, which is largely composed of plastic, is generated today in particularly large quantities. Unlike many conventional heat treatment methods, the method according to the invention does not generate harmful substances and does not produce any new harmful substances such as, for example, dioxins. Rather, the circuit can be closed for any substance and the recycling rate can be significantly increased.

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages of the invention are evident from the dependent claims and are explained in more detail in the following examples and figures.

A supercritical fluid is a fluid having a temperature above the so-called critical temperature and a pressure above the so-called critical pressure, where the points having the critical temperature and the critical pressure in the phase diagram are the critical point. Called. In the supercritical state, no distinction between liquid and gas is possible.
The properties of a supercritical fluid are similar to gas and liquid, depending on temperature and pressure.

In the case of supercritical wet oxidation, various properties of supercritical water: for example, very good solvent behavior for organic materials and gases and good behavior as reaction medium (Cliffo)
rd AA: Chemical destruction using supercritical
water, In: Clark JH (ed): Chemistry of waste Minim
(1995).

In the supercritical region (above 374 ° C. and 22.1 MPa for water), the material properties change. In particular, the density of water is reduced by a factor of about 10 relative to the ambient conditions, and at the same time the dynamic viscosity of the pure water is reduced by a factor of about 20 (density ρ and dynamic FIG. 1 showing the viscosity η as a function of the temperature at a pressure of 25 MPa). Thereby, the density is always still like a liquid, while the viscosity takes the value of a gas.

[0026] Figure 2 shows the dielectric constant ε and the ionic product _{K w} about pure water at a pressure of 25MPa as a function of temperature. The decrease in the permittivity constant ε at supercritical is explained by the decrease in hydrogen bonding conditions according to chemistry, i.e., water always becomes less polar as it approaches the critical point, and at supercritical water almost nonpolar Behaves (Clifford, AA: aa
O.). In addition, the ionic product increases in strength over a power of ten, ie the conductivity increases correspondingly.

The resulting change in solvent behavior is illustrated in FIG. 3, which shows that the organic (K
(W, hydrocarbons) and the solubility of inorganic substances as a function of temperature, measured at supercritical pressures of 22.1-30 MPa. Hydrocarbons become almost indefinitely soluble from the near-critical region, whereas the solubility of inorganic substances decreases strongly above the critical temperature in the opposite direction (Modell,
M .; Paulaitis, ME: Supercritical Fluids; Enviro
nci Sci. Technol .; Vol 16; No. 10, 1982).

An index of the behavior as a reaction medium is shown in FIG. 4 which shows the density ρ of pure water and the diffusion coefficient D of a strongly diluted benzene solution as a function of temperature at a pressure of 25 MPa (Caroll, JC: Ph. D. Thesis, U
niversity of Leeds, UK, 1992). The high diffusion of water within the supercritical range causes the reaction to be determined primarily by kinetics, rather than by mass exchange.

Due to the high solubility of organic substances and gases in supercritical water, a critical reaction system exists between the polymer, water and oxygen in a single phase. With high diffusion, reactions that are too rapid occur, which are generally in the range of minutes, while other thermochemical methods require hours or even days.

When treating solid residuals by supercritical wet oxidation, the solids are dispersed in water and brought to supercritical pressure. Subsequently, the temperature is raised to within the desired range, preferably to the supercritical range.

The organic components go into solution and are partially decomposed hydrolytically. The decomposition is completed by adding an oxidizing agent such as oxygen, H ₂ O ₂ or air. Organic substances are converted to carbon dioxide, water and molecular nitrogen. The halogens present are converted to the corresponding salts. The metals present then serve as cation donors. In addition, the metal oxidizes and catalyzes the reaction. If present, the ceramic component does not affect the chemical process. They are insoluble under all conditions. Similarly, the corresponding salts are insoluble under the usual conditions of supercritical wet oxidation (250-300 MPa, 500-600 ° C.). However, it is also possible to keep the salt in solution with very high pressures up to 1000 MPa.

At the end of the reaction phase, the temperature is reduced and the pressure is again adjusted to ambient pressure. Subsequently, the reaction products can be separated from one another on the basis of the phases “gas”, “liquid” and “solid”.

There are a number of difficulties in processing solids by supercritical wet oxidation. Supercritical water is already high pressure (23-30 bar) and high temperature (400-600
C.) as well as the strongly acidic behavior imposes increased demands on the material. The progress of the reaction as well as attrition by solids make the conditions more severe. A particular disadvantage is the presence of halogen. In this case, the maximum corrosion exfoliation occurs around the critical temperature (T = 374 ° C.) or the pseudo critical temperature (the pseudo critical temperature is, for example, 405 toward a higher temperature depending on the pressure with respect to the pressure of 30 MPa). ° C). One solution is to keep the process parameters as mild as possible, for example by reducing the temperature, and by removing the load due to the cold boundary layer flow along the reactor wall, by means of a corresponding process configuration or reaction control. In the first case, ie, at low temperatures, long residence times are required for the same decomposition rate, thus requiring large equipment. The second example,
Cold boundary layer flow requires costly structural measures.

An additional difficulty in treating solids by supercritical wet oxidation is the sedimentation, ie, the tendency of the particles to settle to the bottom of the equipment section. Due to the altered fluid properties within the supercritical range with respect to the ambient conditions, the settling velocity of the charged solid particles increases significantly. The settling can be avoided by using a horizontal tube reactor. At a suitably high flow rate, the suspension remains stable. Investigations have shown that keeping the suspension stable in supercritical water is less problematic than in liquid water. This is because, as the density decreases, it increases in inverse proportion to the flow rate in the tubular reactor and overcompensates for the high sedimentation velocity (Pilz, S .: Modeling, Design and Scale-Up of an
SCWO Application Treating Solid Residues of Electr
onic Scrap Using a Tubular Type Reactor-Fluid Mech
anics, Kinetics, Process Envelope, VDI-GVC High Pr
essure Chemical Engineering Meeting; 03.-05. Maer
z, Karlsruhe).

[0035] Suspension tube reactors are subject to high attrition by solid particles. The use of devices (valves, measuring devices) creates additional difficulties based on changes in tube inner diameter and changes in the strength of the flow method. Here, plugging occurs with the particles, in particular with the fibers. Due to the high flow rates, a very long reactor and a less compact design result.

FIG. 5 is a principle diagram of a first embodiment of an apparatus for supercritical wet oxidation of a residual substance mixture in two stages. The device comprises an elongated upright high-pressure pump 2, a first heat transfer device 4,
PFR (Plug Flow Reactor; slender tube reactor) 6,
CSTR (Continuously Stirred Tank Reactor; inflated tank with stirring device) 8, second heat transfer device 10
And a pressure relief valve 12. These device parts are interconnected by a series of conduits, as shown schematically.

The mixture of residual substances to be processed in the apparatus, for example, crushed light fractions from electronics scraps or motor vehicle recycling, is ground and suspended in water in a device not shown. This water, together with the particles suspended therein, is fed to a high-pressure pump 2, which brings the pressure close to the critical pressure and to a first heat exchanger 4. In the first heat transfer device 4, heat is supplied from outside to the water having the suspended particles, and the water is heated to a temperature near the critical temperature.

Hot water under pressure, with suspended particles, passes first through the PFR 6 and then through the CSTR 8. In the second heat exchanger 10 from the mixture flowing out of the CSTR 8, heat is extracted for cooling to near ambient temperature, and a pressure relief valve 12 releases the mixture to ambient pressure.

Furthermore, if the mixture of water and residual substances does not initially contain a sufficient amount of oxidizing agent, the PFR
An oxidant, for example oxygen, is supplied at any location before 6 or CSTR 8. The oxidant can also be supplied directly into the CSTR 8 for thorough mixing inside the CSTR 8.

The gaseous reaction products, the salts formed in the reactor and the unreacted solids are separated from the water and recycled separately in further equipment parts, not shown. The remaining water can be fed fresh into the circuit, for example if it still contains impurities that are too expensive to separate.

PFR6 and CSTR8 are substantially composed of three consecutive and partially simultaneous decomposition steps: 1) dissolution of an organic substance, 2) hydrolysis and 3) oxidation of an organic substance. It is configured to be performed in PFR 6 and that step 3) is performed substantially in CSTR 10. This separation is easily possible. Because,
Dissolution occurs significantly faster than oxidation under the same conditions.

A correspondingly constructed PFR 6 is significantly shorter than a tubular reactor in which all three cracking steps have to proceed. PFR6 is indeed abraded by solids conveyed at high speed so as not to settle, but the abrasion is rather acceptable. This is because a small amount of the reactor material is subject to attrition, and thus a small amount of the reactor material needs to be renewed after use. Furthermore, the useful life of the reactor material is extended by the fact that substantially no corrosive reaction products are present in the PFR 6, i.e. there is little corrosive loading. Further, relatively short PFRs 6 cause little occlusion problems.

Hydrolysis, ie the partial decomposition of the reaction starting material by ions present in the water, can be carried out in PFR6 or in CST.
This can be done anywhere in R8. Usually, part of the hydrolysis is performed in the PFR 6 and another part is performed in the CSTR 10. Accordingly, the organic substance between the PFR 6 and the CSTR 8 exists at least as a solution or has already been decomposed into a short-chain polymer.

CSTR 8 has a significantly greater ratio of volume to internal surface area than PFR6. Therefore, CS
The flow rate in TR8 is significantly lower than in PFR6. Due to the significantly lower flow rates, the reactor material of CSTR8 experiences slight attrition. Certainly the reaction products are corrosive, but unless fear of abrasion of strength,
There are many durable materials for CSTR8.

In the CSTR 8, thorough mixing is performed in all the reaction chambers based on the stirrer. Good mixing reduces the reaction time and thus the residence time, which is usually longer for oxidation than the first two decomposition steps. Therefore, C
The STR 8 does not need to have an excessively large volume to achieve sufficient residence time of the material to be degraded. Due to the good mixing, the reaction in the CSTR 10 proceeds more particularly evenly, so that large-scale mechanical devices can be omitted to avoid failures. In the case of PFR6, such an arrangement is indeed necessary, but a small control length, for example a pressure measuring device, is required because of the short structural length.

In addition, in the case of the expanded construction of the CSTR 8, provision of means for inhibiting corrosion or improving the kinetics, such as coatings or inserts, can also be provided by the PFR.
6 is easier. Corrosion inhibiting coatings and inserts which protect the reactor walls, for example by cold zones, allow higher reaction temperatures and correspondingly shorter reaction times.

The volume remaining in the CSTR 8 and the large ratio of volume to internal surface area allows for a very compact design. The space demand for the CSTR 8 is less than the saved length space demand of the PFR 6. Therefore, an extremely compact device as a whole can be realized.

CSTRs themselves have the disadvantage that if the ratio of internal surface area to volume is small, heat can only be introduced and extracted relatively slowly. In this reactor type, a continuous reaction is very difficult to control. However, the cost for controlling the reaction in the CSTR 8 is reduced, since most of the heat of reaction already occurs in the PFR 6 and can be derived from its relatively large surface.

In the CSTR 8, it is not necessary to consider sedimentation. This is because the solids still present are not important for the reaction to take place therein. The particles can simply be precipitated by CSTR8 and later separated.

FIG. 6 shows a second embodiment of the device for supercritical wet oxidation of the residual material mixture in two stages, which is connected between the PFR 6 and the CSTR 8 with the device in FIG. Only the additional high-pressure separator 14 is distinguished. In the high-pressure separator 14, the solids leaving the PFR 6 are separated in order to completely avoid the attrition load of the following equipment parts.

In summary, splitting the reaction into two sections combines the individual advantages of the two continuously working reactor types PFR and CSTR. In the first section, the solid components are transferred to the fluid phase, wherein the decomposition of organic substances is neglected. In the second category, complete decomposition of the hazardous substances is performed.

At this time, first, a PFR having a high flow rate is used for stable suspension conveyance. The resulting temperature peak derives through a narrow shape. Subsequently, a CSTR is used, which can be made significantly more compact than a PFR for the same reaction residence time. In addition, the required reduced residence time with good mixing is achieved.

[Brief description of the drawings]

FIG. 1 is a graph showing density and dynamic viscosity for pure water as a function of temperature at a pressure of 25 MPa.

FIG. 2 is a graph showing the dielectric constant and ionic product for pure water at a pressure of 25 MPa as a function of temperature.

FIG. 3 is a graph showing the solubility of organic and inorganic substances in water as a function of temperature at pressures of 22.1-30 MPa.

FIG. 4 is a graph showing the density of pure water and the diffusion coefficient of strongly diluted benzene solution as a function of temperature at a pressure of 25 MPa.

FIG. 5 is a principle view of an apparatus for supercritical wet oxidation of a residual substance mixture in two steps according to a first embodiment.

FIG. 6 is a principle diagram of an apparatus for supercritical wet oxidation of a residual substance mixture in two stages according to a second embodiment.

[Explanation of symbols]

2 pump device, 4 heating device, 6 tube reactor,
14 Particle separator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Margit Feh Germany Ulm Karlstrasse 29/1 (72) Inventor Korea Reebstock Germany Federal Ulm Peony Ashtrath 27 F-term (reference) 4D004 AA22 AA26 CA04 CA39 CB04 CB21 DA02 DA06 DA07

Claims (10)

[Claims] An organic and inorganic component is suspended in water, the water is brought into a near critical state or a supercritical state, and the particles comprising the organic and inorganic components are passed through a tubular reactor in this state. In a method for supercritical wet oxidation of a residual substance mixture to be contained, a tubular reactor (6) is configured such that organic components are not substantially oxidized therein and are substantially dissolved in water, and The reactor starting material was designed to have a significantly smaller ratio of internal surface area to volume than the tubular reactor at near and supercritical conditions and to substantially completely oxidize organic components therein. Second reactor (8)
Supercritical wet oxidation method characterized by passing through. 2. The method according to claim 1, wherein the particles are kept suspended in the tubular reactor by a flow rate of water. 3. The process as claimed in claim 1, wherein the starting material of the tubular reactor together with the particles still present is passed through the second reactor. 4. The process as claimed in claim 1, wherein the particles contained in the starting material of the tubular reactor (6) are separated, and then the other starting materials are passed through the second reactor (8). 5. The process as claimed in claim 1, wherein the residue mixture is an electronic scrap or a crushed light fraction from an automobile recycling ring. 6. An apparatus for supercritical wet oxidation of a mixture of residual substances containing particles of organic and inorganic components suspended in water, the apparatus comprising water with particles suspended therein. In a type having a pump and a heating device (2, 4) configured to be in a near critical state or a supercritical state, and a second reactor (6) connected downstream, a tubular reactor includes: An organic component is not substantially oxidized therein, is configured to be substantially dissolved in water, and a second reactor (8) is connected to the rear of the tubular reactor;
The supercritical wet process is characterized in that the reactor has a significantly smaller internal surface area to volume ratio than a tubular reactor and is configured such that organic components are substantially completely oxidized inside. Oxidation equipment. 7. The apparatus according to claim 6, wherein the tubular reactor (6) is configured for a high flow rate in order to keep the particles more floating in the water flow. 8. The device according to claim 6, wherein the second reactor has a stirring device. 9. The outlet of the tubular reactor (6) and the inlet of the second reactor (8) are directly connected to one another.
An apparatus according to any one of claims 1 to 8. 10. The process according to claim 6, wherein the outlet of the tubular reactor and the inlet of the second reactor are connected to one another via a particle separator. The described device.